Re: [PATCH 2/4] KVM: nSVM: propagate the NPF EXITINFO to the guest

[Avi Kivity]

On 09/02/2014 07:46 PM, Paolo Bonzini wrote:
> */
> > >   		if (unlikely(real_gfn == UNMAPPED_GVA))
> > >   			goto error;
> > > @@ -1974,10 +1974,28 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
> > >   {
> > >   	struct vcpu_svm *svm = to_svm(vcpu);
> > >   
> > > -	svm->vmcb->control.exit_code = SVM_EXIT_NPF;
> > > -	svm->vmcb->control.exit_code_hi = 0;
> > > -	svm->vmcb->control.exit_info_1 = fault->error_code;
> > > -	svm->vmcb->control.exit_info_2 = fault->address;
> > > +	/*
> > > +	 * We can keep the value that the processor stored in the VMCB,
> > > +	 * but make up something sensible if we hit the WARN.
> > > +	 */
> > > +	if (WARN_ON(svm->vmcb->control.exit_code != SVM_EXIT_NPF)) {
> > > +		svm->vmcb->control.exit_code = SVM_EXIT_NPF;
> > > +		svm->vmcb->control.exit_code_hi = 0;
> > > +		svm->vmcb->control.exit_info_1 = (1ULL << 32);
> > > +		svm->vmcb->control.exit_info_2 = fault->address;
> > > +	}
> > Its been a while since I looked into this, but is an injected NPF exit
> > always the result of a real NPF exit?
> I think so, but that's why I CCed you. :)

It could always be the result of emulation into which L0 was tricked.  I 
don't think it's a safe assumption.

> > How about an io-port emulated on
> > L1 but passed through to L2 by the nested hypervisor. On emulation of
> > INS or OUTS, KVM would need to read/write to an L2 address space,
> It would need to read/write to *L1* (that's where the VMCB's IOIO map
> lies), which could result into a regular page fault injected into L1.
>
> Paolo
>
> > maybe
> > causing NPF faults to be injected. In this case an IOIO exit would cause
> > an injected NPF exit for L1.
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